Modelling the potential impact of spatially targeted natural flood management at the landscape scale for a rural UK catchment.

Abstract

Flooding has a significant impact across a large portion of the United Kingdom. Many flood risk reduction schemes focus on hard engineering approaches which are capable of protecting a large amount of infrastructure and properties. However, for a sparsely populated rural catchment that does not meet central cost-benefit criteria required for hard engineering schemes, the potential for a reduction in flood risk through a sustainable, lower-cost approach can create a viable alternative. Natural flood management is an approach that is growing in application in the UK with regards to helping reduce flood risk at a catchment scale; however there is a need for the potential impacts on flooding and wider catchment dynamics of the techniques and interventions to be quantified before potential schemes can attain funding; there is currently a lack of empirical evidence available to support this quantification.

This research project used a combination of a physically-based, fully spatially-distributed hydrological model (CRUM3), a risk-based model focused on hydrological connectivity (SCIMAP-Flood) and stakeholder engagement to develop and model natural flood management interventions at the landscape scale. The process allowed for the quantification of the impact of a variety of natural flood management interventions at reducing the maximum discharge for the simulated flooding event. These methods were applied to the study area of the River Roe catchment in Cumbria, a 69km2 rural catchment that experienced significant flooding events in both 2005 and 2013.

The effectiveness of a variety of flood risk reduction scenarios in the River Roe catchment were tested; these scenarios included spatially targeted land cover change to attenuate overland flow, soil aeration to mitigate soil compaction issues commonly associated with rural catchments and woody debris dams to slow the delivery of water downstream. It was established through the research that a significant proportion of land has to be acted upon to have a noticeable reduction in the maximum discharge produced during a flood event; as a consequence of this finding, large-scale soil aeration to keep soil compaction to low levels throughout the catchment is arguably the most effective natural flood management measure for this catchment.